Self-tuning brain implant

Medical Innovations

Self-tuning brain implant

NIH BRAIN Initiative-funded research is a key first step to improving deep brain stimulation, treating patients with Parkinson’s disease.

Elizabeth Engler Modic (Edited by)

Stimulating and sensing electrodes are implanted in the brain and connect to a small computer under the skin. Data from this computer can be read by an external device. Image courtesy of Ken Probst/Starr lab

Deep brain stimulation uses a surgically implanted thin-wire electrode to manage Parkinson’s disease symptoms. Traditional deep brain stimulation delivers constant stimulation to a part of the brain called the basal ganglia; however, this can lead to unwanted side effects that require clinician reprogramming. A new method is adaptive, so the stimulation delivered is responsive in real time to signals received from the patient’s brain.

In a short-term feasibility trial, two patients with Parkinson’s received fully implanted, adaptive deep brain stimulation devices. They differ from traditional ones in that they can monitor and modulate brain activity. Sensing comes from an electrode implanted over the primary motor cortex, a part of the brain critical for normal movement. Signals from this electrode then feed into a computer program embedded in the device, which determines whether to stimulate the brain.

Researchers taught the program to recognize a pattern of brain activity associated with dyskinesia, or uncontrolled movements that are a side effect of deep brain stimulation in Parkinson’s disease, as a guide to tailor stimulation. Stimulation was reduced when it identified dyskinesia-related brain activity and increased when brain sensing indicated no dyskinesia.

Results of initial, short-term studies suggested that this adaptive approach was equally effective at controlling symptoms as traditional deep brain stimulation. Doctors and patients noticed no differences in the improvement in movement under adaptive stimulation versus constant, open-loop stimulation set manually by the researchers. Because adaptive deep brain stimulation did not continuously stimulate the brain, the system lowered battery use by 40%. The short time periods when movement was assessed did not permit comparison of the two deep brain stimulation paradigms relative to incidence of dyskinesia, but researchers hope that variable stimulation will also translate into a reduction in adverse effects when tested throughout longer time periods.

“Other adaptive deep brain stimulation designs record brain activity from an area adjacent to where the stimulation occurs, in the basal ganglia, which is susceptible to interference from stimulation current,” says Philip Starr, M.D., Ph.D., professor of neurological surgery, University of California, San Francisco, and senior author of the study. “Instead, our device receives feedback from the motor cortex, far from the stimulation source, providing a more reliable signal.”

Many patients with Parkinson’s disease who would benefit from deep brain stimulation are difficult to treat because too much stimulation can cause dyskinesia, so finding the correct level of stimulation is like trying to hit a constantly moving target. An adaptive system such as this could offer an effective alternative and may also limit adverse effects of traditional deep brain stimulation.